A list that is automatically stored in order

OrdList.hs

module OrdList (empty, fromList, insert, toList, OrdList) where
import Data.List as L (span)

data OrdList a = OrdList [a] deriving (Show)


empty :: OrdList a
empty = OrdList []

insert :: (Ord a) => a -> OrdList a -> OrdList a
insert x ol =
  let (before, after) = L.span (\el -> el <= x) $ toList ol
  in OrdList $  before ++ [x] ++ after

fromList :: Ord a => [a] -> OrdList a
fromList xs =
  if null xs then empty else insert (head xs) (fromList $ tail xs)

toList :: OrdList t -> [t]
toList xs =
  let OrdList xs' = xs in xs'